Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

Summary

X-ray spectra provide a wealth of information on high temperature plasmas. This manuscript presents the operation of a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma.

Abstract

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity with good spatial and time resolution. However, benchmarking atomic code modeling of X-ray spectra obtained from well-diagnosed laboratory plasmas is important to justify use of such spectra to determine plasma parameters when other independent diagnostics are not available. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma. In addition, this manuscript covers a laser blow-off system that can introduce such ions to the plasma with precise timing to allow for perturbative studies of transport in the plasma.

Introduction

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma off-axis, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity inside the plasma with good spatial and time resolution^1,2. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a ....

Protocol

1. Choosing Appropriate Spectral Lines

1. Choose appropriate emission lines that will determine the quality of obtained data. Figure 8 shows which noble gas emission lines will be relevant at different values for the electron temperature.
   1. Note that the ionization state and line ratios are determined by the competition of ionization, collisional excitation, radiative recombination and dielectric recombination. These processes can vary with plasma temperature and density. See Figure 9 for an example of this variation.
2. Refer to other published works for the wavelengths and relative strengths o....

Results

A representative data sample from the pixel detector for one time bin for the He-like argon spectrum is shown in Figure 17. The spectral lines, bent into an elliptical shape by the spherical crystal, are clearly visible. The top detector has a broken detector panel, and there are some dead pixels scattered across all of the detectors. Data from the broken detector panel should be ignored. Slices from the detector showing the measured spectra and results of the spectral fi.......

Discussion

The data generated by this technique can be used in a wide variety of experimental studies. Ion temperature and toroidal velocity profiles can be used in a wide range of transport studies, including intrinsic self-generated plasma rotation and non-local perturbative effects. Measuring spectra of injected impurities through laser blow-off can also provide important information about the transport of impurities in the plasma, as was done in Howard et al. 2011¹⁰. At this time, no other plasma diagnostic .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
PILATUS 100k Detector System	DECTRIS	100k	Superseded by newer PILATUS3 detectors
Bragg Crystals	Kurchaov Institute	Custom Part
CaF2 Slides	LeBow	Custom Part
High Purity Argon	Airgas	AR HP300	Any high purity argon should work
Be window	Brush Wellman Electrofusion Products / Motion Hightech	Custom part